1. Field of the Invention
The present invention relates to an apparatus for improving the operating capability of a construction machine during a fine operation mode and a method for the same and, more particularly, to an apparatus capable of preventing a merged hydraulic fluid from being supplied into a hydraulic actuator and capable of increasing the pressure of a hydraulic fluid being supplied into the hydraulic actuator during operation of the construction machine in the fine operation mode.
2. Description of the Prior Art
Generally, a construction machine, such as an excavator, is provided with a first hydraulic pump for operating a boom cylinder and a second hydraulic pump for operating an arm cylinder. The first hydraulic pump and the second hydraulic pump drive the boom cylinder and the arm cylinder using a driving force supplied from an engine of the construction machine, respectively.
When an operator wants to perform a desired work using the construction machine as described above, the operator selects a desired operation mode. Selection of the proper operation mode is typically dependent on the working conditions, such as the load conditions involved in performing the above work. In other words, when the operator does not wish to perform an operation, the operator chooses an idle mode as the rotation mode of the engine. In the idle mode, all of the hydraulic fluid is bypassed to the tank. When the construction machine needs to be finely or precisely operated, the operator chooses a fine operation mode as the rotation mode of the engine. Alternately, when the operator wants to perform general work using the construction machine, the operator chooses a standard operation mode as the rotation mode of the engine. Finally, when the operator wants to perform heavy work consuming a large driving force, the operator chooses a heavy operation mode as the rotation mode of the engine.
U.S. Pat. No. 5,469,646 issued to Fujitoshi Takamura on Nov. 28, 1995, discloses a conventional fine operation mode changeover device for a hydraulic excavator. During the operation of the hydraulic excavator in the fine mode, rotational speed of the engine is set to a relatively low speed and the angle of a wobble plate is decreased. Accordingly, the engine of the hydraulic excavator is driven at a relatively low RPM count, such as about 1,500 RPM. Consequently, a discharge flow rate of the pump decreases, and thereby the operator of the heavy excavator can precisely operate the heavy excavator.
However, in these conventional construction machines, such as the above hydraulic excavator, when the operator operates the boom cylinder without operating the arm cylinder in the fine operation mode, a second hydraulic fluid supplied from the second hydraulic pump is merged with the first hydraulic fluid supplied from the first hydraulic pump. This merged hydraulic fluid is then supplied to the boom cylinder. Likewise, when the operator operates the arm cylinder without operating the boom cylinder in the fine operation mode, the first hydraulic fluid is merged with the second hydraulic fluid. Similarly, the merged hydraulic fluid is then supplied to the arm cylinder.
Accordingly, the merged hydraulic fluid supplied to the arm cylinder or the boom cylinder causes the flow rate of the hydraulic fluid being supplied to the arm cylinder or the boom cylinder to be increased. Since the operating speed of the arm cylinder or the boom cylinder is increased, it is difficult to perform a precise work. Furthermore, in conventional construction machines, such as the above hydraulic excavator, when the operator operates the construction machine in the fine operation mode, a relatively large load is applied to the construction machine. As a result, the operating capability deteriorates.